The third "class" of mail was founded in 1863. Prior to that date circulars, handbills, and other material were charged the same postage rates as magazines.

For all practical purposes third-class mail between 1863 and 1879 became a catch-all category. Within the classification was a miscellany of matter some of which was accorded special rates.

With the designation of a fourth class of mail in 1879 some of the matter which was embraced by the former third class was shifted to fourth class. Printed matter other than regular newspapers and periodicals remained third class, while merchandise and other mailable matter became fourth class.

Later the distinction between third and fourth classes was changed from type of matter to a weight basis. First, in 1914 parcels of miscellaneous printed matter, if weighing over 4 pounds, were shifted to fourth class; in the same year books over 8 ounces were also placed in fourth class. Finally in 1925, all matter not in the first or second classes weighing 8 ounces or less was placed in the third class and that weighing over 8 ounces in the fourth class. In the same year catalogs not weighing over 8 ounces were given a special third-class rate.

In 1928 a special "bulk rate" was made applicable to separately addressed identical pieces of third-class matter mailed at one time in quantities of at least 20 pounds or 200 pieces. Facing and separation by states, cities, etc., were required of the mailer.

Like second-class mail, rates of postage for third-class matter have been subject to relatively little change since 1879. For a period of 46 years the basic rate was 1 cent for each 2 ounces. This was increased in 1925 to 11/2 cents, and finally in 1948 to 2 cents for the first 2 ounces and 1 cent for each additional ounce for mailings under the piece rate. The most important change was the inauguration of a "bulk mailing service" mentioned above, which served to lower third-class rates for larger mailings of identical pieces. The initial rate was 12 cents a pound, which was increased in 1949 to 14 cents.

By far the largest users of third-class mail are advertisers. Reflecting the overall increase in national advertising, the volume of advertising matter sent through the mail has increased sharply over the years. In fiscal 1955 the Department handled over 15 billion pieces of third-class mail. The impact of these mailings on sales of goods and services in the United States is incalculable, but their influence probably amounts to billions of dollars each year.